Musnad Abu Ya'la al-Mawsili 1:68

Ubayd Allah ibn Umar narrated to us, Zaidah ibn Abi al-Ruqad narrated to us, Ziyad al-Numayri narrated to me, from Anas: That Abu Bakr entered upon the Prophet, may Allah bless him and grant him peace, while he was sorrowful. The Prophet, may Allah bless him and grant him peace, said to him, "What is the matter with me that I see you sorrowful?" He said, "O Messenger of Allah, I was with a cousin of mine last night, so-and-so, and he was struggling with his soul (dying)." He said, "Why did you not prompt him to say 'La ilaha illa Allah' (There is no god but Allah)?" He said, "I did, O Messenger of Allah." He said, "And did he say it?" He said, "Yes." He said, "Paradise has become incumbent for him." Abu Bakr said, "O Messenger of Allah, how is it for the living?" He said, "It is more destructive to their sins. It is more destructive to their sins."